This application claims the benefit of German patent application DE19910279.1, filed Mar. 9, 1999, herein incorporated by reference.
1. Field of the Invention
The present invention relates to a bearing of a spinning rotor of an open-end spinning apparatus.
2. Background of the Invention
In open-end rotor spinning machines, spinning assemblies are known in which the spinning rotor revolving at high rpm is braced with its rotor shaft in the bearing gap of a support disk bearing arrangement and is fixed via an axial bearing disposed on the end. The support disk bearing arrangement includes two pairs of support disks whose axes are transposed such that an axial thrust is exerted on the rotor shaft that urges the rotor shaft in contact with the mechanical axial bearing.
This type of bearing for open-end spinning rotors is described for instance in published, nonexamined German Patent Application DE-OS 25 14 734, and has been proven itself in practice to allow rotor speeds of 100,000 rpm or more. However, a disadvantage of this type of spinning rotor bearing is that, because of the transposition of the support disks, increased friction occurs between the rotating peripheral surfaces of the support disks and the rotor shaft, which leads to heating of the peripheral surfaces of the support disks. This frictional heat not only causes considerable stress on the peripheral surfaces of the support disks, but also requires additional energy to overcome this friction. Furthermore, the known mechanical axial bearings are subject to not inconsiderable wear, even if they are lubricated as prescribed.
Attempts have therefore already been made in the past to replace these mechanical axial bearings with wear-free axial bearings, such as air bearings or magnetic bearings. However, since even air bearings require an axial thrust of the rotor shaft in the direction of the axial bearing, it has not been possible to overcome most of the above-described fundamental problems with air bearings.
In German Patent Disclosure DE 195 42 079 A1, an axial magnetic bearing assembly is described in which some of the magnetic bearing elements are disposed in stationary fashion in the housing of an axial bearing, while other magnetic bearing elements are disposed detachably on the rotor shaft of the spinning rotor. Various different ways of binding the magnetic bearing elements, which rotate with the spinning rotor, to the rotor shaft have been proposed. Some of these variants pertain to a nonpositive, and others to a positive fastening of the jointly rotating magnetic bearing elements, which can easily be detached as needed.
Although these known magnetic bearing arrangements provide correct axial fixation of the rotor shaft on the support disk arrangement and moreover assure that as needed the spinning rotor can easily be installed and removed, it has nevertheless been found that the positive fastening of the magnetic bearing component to the rotor shaft, which is easily detachable as needed and is advantageous in principle, still needs improvement. In particular, the fastening of the jointly rotating magnetic bearing elements to the rotor shaft is problematic in such magnetic bearing arrangements, because stringent demands are made on the quality of the balance of this connection due to the high rpm of the spinning rotor.
An open-end rotor spinning apparatus with a permanent- magnetic axial bearing is also known from Austrian Patent AT 270 459. In this bearing arrangement, several magnetic ring inserts are disposed on the end of the rotor shaft of a spinning rotor, and opposite thereto are pole pieces of a permanent magnet that is pivotably supported in this region. Such an arrangement achieves a focusing of the magnetic lines of force of the permanent magnet which leads to a relatively rigid fixation of the rotor shaft in the bearing nip of a support disk bearing.
A disadvantage of a magnetic bearing arrangement embodied in this manner, however, is that the ring inserts disposed on the rotor shaft have a markedly greater diameter than the rotor shaft itself. Since the markedly larger-diameter ring inserts make it considerably more difficult or impossible to install and remove the spinning rotor, and especially to mount it on the front, this known magnetic bearing arrangement has not become established in practice.
German Patent Disclosure DE 30 47 606 A1 discloses a bearing for a spindle of a textile machine which revolves at relatively high rpm. This spindle is braced in the radial direction via a three-point bearing arrangement similar to a support disk bearing and is secured in the axial direction by a magnetic bearing. On its end, the spindle has a reduced-diameter bearing region with two ferromagnetic ring inserts. A cuff made of a nonmagnetic material is fixed to the bearing housing, and an annular permanent-magnetic element is fitted into this cuff and is enclosed by lateral pull disks. In the installed state of the spindle, the ferromagnetic ring inserts of the spindle shaft face the pole disks of the permanent-magnetic element that is fixed in the static bearing element.
Although these known embodiments enable relatively easy installation and removal of the spindles in the axial direction, the apparatus has not become established in practice because of its lack of axial bearing rigidity.
A bearing of a spinning rotor of an open-end spinning apparatus is also known from German Patent Disclosure DE 197 29 191 A1, in which the rotor is radially supported in the bearing nip of a support disk bearing and is axially positioned by a magnetic axial bearing. The axial bearing has a static bearing component with at least two permanent-magnetic rings defined on both sides by pole disks. These permanent-magnetic rings are disposed in a bearing body such that in the installed state, identical poles face one another (N/N or S/S). The rotor shaft has at least three ferromagnetic ribs disposed at a distance from the pole disks.
German Patent Disclosure DE 197 29 191 A1 also indicates that the bearing housing is lowered with its center axis relative to the center axis of the rotor shaft defined by the position of the bearing nip of the support disks. As a result, an upward-oriented radial force component is imparted to the rotor shaft in the region of the axial bearing. Thus, when cleaning of the rotor, the rotor is no longer pressed into the bearing nip by the contact pressure roller, which presses the lengthwise-extending tangential belt that drives the rotor shaft, but instead is retained in a horizontal position. However, this radial component has an adverse effect during the drive of the rotor.
It is therefore an object of the present invention to provide an improved bearing of the basic type described above for use in a spinning rotor.
This object is attained according to the invention by a bearing for a shaft of a spinning rotor of an open-end spinning apparatus which basically comprises a support disk bearing defining a bearing nip for radially supporting the rotor shaft and a magnetic axial bearing for axially positioning the rotor shaft. The axial bearing has a static bearing component with at least two axially polarized permanent-magnetic rings bounded on opposite sides by pole disks, the permanent-magnetic rings being disposed in a bearing body such that corresponding magnetic poles face one another. The rotor shaft has at least three ferromagnetic annuli at respective spacings from the pole disks. The support disk bearing is disposed in relation to the static bearing component of the axial bearing to retain the rotor shaft in the bearing nip with a center axis of the rotor at an offset in the direction of the bearing nip from a center axis of the static bearing component. The static bearing component includes an engagement surface outwardly of the magnetic rings and the pole disks toward the support disk bearing and on the side of the support disk bearing remote from the bearing nip. The engagement surface faces the rotor shaft over an angular extent of at least about 45xc2x0 of the rotor shaft and has a wear-protected surface layer for reducing the coefficient of friction of the engagement surface, with the wear-protected surface layer being spaced from the rotor shaft during operation by no more than half the smallest spacing between the pole disks and the ferromagnetic annuli.
The offset according to the invention in the support disk bearing of the rotor relative to the static bearing component of the axial bearing assures improved guidance of the rotor in the bearing nip of the support disks. Above all, the concentricity of the rotor is enhanced, and the influence of transit-time-associated changes from flexing work in the support disk lining decreases, because the adhesion of the rotor shaft to the support disk lining inside the bearing nip is improved. As a result, the invention thus makes it possible to further increase the possible rotor rpm and thus to improve productivity.
The radial force component on the rotor shaft, attained by the bearing offset, leads to an increased tendency of the rotor shaft to tilt out of the bearing nip of the support disks while the rotor is being cleaned. To prevent the ferromagnetic annuli of the rotor shaft from then coming into contact with the pole disks disposed between the magnets, an engagement surface with a wear-protected surface layer that reduces the coefficient of friction is provided on the side of the bearing remote from the bearing nip (this and subsequent directional indications with reference to the bearing nip being understood to mean radially relative to the rotor shaft and hence the rotor axis) and at a suitably slight spacing from the rotor shaft. At least when the rotor is cleaned, the rotor shaft comes into contact with this surface layer and is then supported on it, yet the aforementioned contact between the annuli and pole disks does not occur.
The reduction in the coefficient of friction by the surface layer, upon rotation of the rotor during cleaning, does not lead to a perceptible or even harmful heating of the rotor shaft. Such heating could, particularly if the spaces (typically grooves) between the annuli of the rotor shaft are filled with a material that is not temperature resistant, could cause it to melt and could cause the entire bearing region to stick together. The embodiment as a wear-protected surface assures that the layer wears down only very slowly if at all, so that the position of the engagement surface does not perceptibly change, and the properties of reducing the coefficient of friction are preserved.
The disposition of the engagement surface, or of the wear-protected surface layer that reduces the coefficient of friction, on a ring insert makes it easy to replace the ring insert. It is accordingly also possible to make this entire ring insert of this material.
The radial adjustability of the ring insert allows adjusting the annular gap as needed. A narrower annular gap on the side remote from the bearing nip is advantageous, because canting of the rotor shaft during cleaning of the rotor cup is as a result even more restricted.
Because the rotor is pressed during cleaning into the axial bearing by a drive mechanism of the cleaning unit (e.g. a traveling service unit) acting on the rotor cup, it is advantageous to provide a support surface axially in the region of the end of the rotor shaft as well. On the one hand, this arrangement limits the axial motion of the rotor and, on the other hand, because this support surface also has a wear-protected surface layer that reduces the coefficient of friction, it minimizes thermal stress on the rotor shaft in the region of the axial bearing.
Because the rotor is tilted during cleaning, the rotor can also be supported not only on the aforementioned support surfaces but additionally by engagement of its shaft end on the side of the shaft toward the bearing nip on a support face which in turn is also provided with a wear-protected surface layer that reduces the coefficient of friction.
The last two support surfaces mentioned are advantageously formed by a sleeve retained in a receptacle. This sleeve can likewise entirely comprise the anti-friction wear-protected material. An economical material having these properties is for example a carbon fiber or graphite material.
The indicated ratio between the center axis offset and the difference in diameter between the pole disks and the annuli defines the offset of the center axis that is advantageous according to the invention. Relative to the bearing arrangement of the invention, corresponding absolute values thus advantageously result.
The dimensioning of the magnetic rings and pole disks is preferably optimized for the corresponding dimensions of one another and the bearing rigidity. For example, the offset of the center axis of the rotor from the center axis of the static bearing component is from about 0.2 to about 1.0 mm, and preferably from about 0.25 to about 0.4 mm. The requisite bearing rigidity also exists even though on the side of the static bearing component remote from the bearing nip, the bearing offset causes markedly larger air gaps exist between the annuli and the pole rings, which weaken the magnetic field. In principle, the relationships should be selected such that, for an increased cross sectional area of the magnets, correspondingly increased cross-sectional areas of the pole disks are selected, in order to prevent magnetic saturation of the pole disks that limits the magnetic flux attainable by the magnets.
To attain the requisite magnetic flux for the functionally required bearing rigidity, in conjunction with the existing installation space, it is advantageous to select rare earth as the magnetic material.
It is advantageous for a pole disk that is located between magnetic rings to have approximately twice the thickness of the outer pole disks, because this pole disk conducts the magnetic flux from both adjacent magnets. Otherwise, saturation, with the aforementioned consequences, would be expected in the region of this middle pole disk as well.
The bearing rigidity can also be optimized if the annuli and pole disks have the same width. It is also advantageous for the development of the magnetic field if the opposed edges of the pole disks and the annuli are nonrounded.
The grooves between the annuli of the rotor shaft are preferably filled with a nonmagnetic material, which may advantageously be copper or copper compounds which have better heat resistance than plastic. However, still other known nonmagnetic metal materials can also be used, such as tin, zinc or aluminum.
To achieve the requisite bearing rigidity even when little space is available, rare earth magnets are highly advantageous.
Nonrounded edges of pole disks and the annuli improve the magnetic flux density and thus enhance the contribution to increasing the magnetic rigidity.
As one alternative embodiment, the rotor shaft has a constant diameter over its entire length, that is, including the region of the axial bearing, which leads to advantages in terms of production costs. As a second alternative, a graduation of the rotor shaft diameter in the region of the axial bearing can be considered; at high rotor speeds, in particular above 150,000 rpm, this improves the concentricity of the rotor because of the significant increase in the natural frequency via the operating rpm. The absolute depth of the grooves used for machining out the annuli decreases accordingly, to assure the stability of the rotor shaft in the region of the axial bearing.
By means of dimensioning the permanent-magnetic rings according to the invention in conjunction with the pole disks and the annuli width, the axial bearing rigidity required for secure, reliable, safe function can nevertheless be maintained.
Further details of the invention will be understood from exemplary embodiments described below in conjunction with the drawings.